Dustin L. Dalluge

Distinguishing primary and secondary reactions of cellulose pyrolysis

The objective of this study was to elucidate primary and secondary reactions of cellulose pyrolysis, which was accomplished by comparing results from a micro-pyrolyzer coupled to a GC-MS/FID system and a 100 g/hr bench scale fluidized bed reactor system. The residence time of vapors in the micro-pyrolyzer was only 15-20 ms, which precluded significant secondary reactions. The fluidized bed reactor had a vapor residence time of 1-2 s, which is similar to full-scale pyrolysis systems and is long enough for secondary reactions to occur. Products from the fluidized bed pyrolyzer reactor were analyzed using a combination of micro-GC, GC-MS/FID, LC-MS and IC techniques. Comparison between the products from the two reactor systems revealed that the oligomerization of leglucosan and decomposition of primary products such as 5-hydroxymethyl furfural, anhydro xylopyranose and 2-furaldehyde were the major secondary reactions occurring in the fluidized bed reactor. This study can be used to build more descriptive pyrolysis models that can predict yield of specific compounds.

Pyrolytic Sugars from Cellulosic Biomass

Depolymerization of cellulose offers the prospect of inexpensive sugars from biomass. Breaking the glycosidic bonds of cellulose to liberate glucose has usually been pursued by acid or enzymatic hydrolysis although a purely thermal depolymerization route to sugars is also possible. Fast pyrolysis of pure cellulose yields primarily the anhydrosugar levoglucosan (LG) whereas the presence of naturally occurring alkali and alkaline earth metals (AAEMs) in biomass strongly catalyzes ring-breaking reactions that favor formation of light oxygenates. Here, we show a method of significantly increasing the yield of sugars from biomass by purely thermal means through infusion of certain mineral acids (phosphoric and sulfuric acid) into the biomass to convert the AAEMs into thermally stable salts (particularly potassium sulfates and phosphates). These salts not only passivate AAEMs that normally catalyze fragmentation of pyranose rings, but also buffer the system at pH levels that favor glycosidic bond breakage. It appears that AAEM passivation contributes to 80 % of the enhancement in LG yield while the buffering effect of the acid salts contributes to the balance of the enhancement.

Continuous production of sugars from pyrolysis of acid-infused lignocellulosic biomass

Although pyrolysis of carbohydrate-rich biomass should theoretically yield large amounts of sugar, the presence of alkali and alkaline earth metals (AAEMs) in most biomass prevents this from happening. Even in small amounts, AAEM strongly catalyzes the fragmentation of holocellulose to light oxygenates compared to the thermally-induced breaking of glycosidic bonds that yield anhydrosugars. The concept of AAEM passivation, by which the catalytic activity of AAEMs can be suppressed to enhance thermal depolymerization of lignocellulose to sugars, has been previously established at the microgram scale using batch reactors. The feasibility of increasing sugar yield via AAEM passivation has not been previously demonstrated at the kilogram scale in a continuous flow reactor. The goal of this research is to demonstrate the enhanced production of sugars from AAEM passivated feedstocks in a continuous auger pyrolyzer at the kilogram scale. Alkali and alkaline earth metal passivation prior to pyrolysis increased total sugars from red oak by 105% compared to conventional pyrolysis, increasing from 7.8 wt% to 15.9 wt% of feedstock. Light oxygenates and non-condensable gases (NCGs) simultaneously decreased 45%, from 27.1 wt% to 14.7 wt% of feedstock as a result of AAEM passivation. Similarly, AAEM passivation of switchgrass increased total sugars by 259%, from 4.5 wt% to 16.2 wt% of feedstock, while the light oxygenates and NCGs decreased by 48%, from 20.0 wt% to 10.5 wt% of feedstock. An undesirable outcome of AAEM passivation was an increase in char production, increasing by 65% and 30% for pyrolysis of red oak and switchgrass, respectively. Loss of lignin-derived phenolic compounds from the bio-oil can explain 67% and 38% of the increase in char for red oak and switchgrass, respectively. The remaining 33% char increase for red oak (3.1 wt% char) and 62% char increase for switchgrass (4.0 wt% char) appear to be from carbonization of sugars released during pyrolysis of acid-infused biomass.

Physicochemical properties of bio-oil and biochar produced by fast pyrolysis of stored single-pass corn stover and cobs.

Short harvest window of corn (Zea mays) stover necessitates its storage before utilization; however, there is not enough work towards exploring the fast pyrolysis behavior of stored biomass. This study investigated the yields and the physicochemical properties (proximate and ultimate analyses, higher heating values and acidity) of the fast pyrolysis products obtained from single-pass stover and cobs stored either inside a metal building or anaerobically within plastic wraps. Biomass samples were pyrolyzed in a 183 cm long and 2.1cm inner diameter free-fall fast pyrolysis reactor. Yields of bio-oil, biochar and non-condensable gases from different biomass samples were in the ranges of 45-55, 25-37 and 11-17 wt.%, respectively, with the highest bio-oil yield from the ensiled single-pass stover. Bio-oils generated from ensiled single-pass cobs and ensiled single-pass stover were, respectively, the most and the least acidic with the modified acid numbers of 95.0 and 65.2 mg g(-1), respectively.